1. Field of the Invention
The invention relates to a fuel injection system for internal combustion engines, with a high-pressure fuel pump, a common rail, at least one injector, and a presupply pump, in which the high-pressure fuel pump supplies fuel to the injector(s) by means of the common rail, with a control of the delivery pressure of the presupply pump, with a return line for conveying fuel away from the injector(s) and/or from the high-pressure fuel pump, and with a pressure control in the return line.
2. Description of the Prior Art
The operating behavior of injectors, of the pressure control of the common rail, and of the high-pressure pump of common rail fuel injection systems depend among other things on the back pressure in the return line. Therefore, in the known fuel injection systems, the pressure in the return line is controlled by pressure-holding valves inserted into the return line or by a pressure control valve connected in parallel to a tank jet pump in the fuel tank. These pressure controls depend on the ambient pressure and the fuel return, which is in turn a function of the operating point of the internal combustion engine.
The object of the invention is to achieve a pressure control in the return line with improved control performance.
This object is attained according to the invention by means of a fuel injection system for internal combustion engines with a high-pressure fuel pump, a common rail, at least one injector, and a presupply pump, in which system the high-pressure fuel pump supplies the injector(s) with fuel by means of the common rail, the presupply pump delivers fuel from a tank to the high-pressure fuel pump, with a control of the delivery pressure of the presupply pump. A return line conveys fuel away from the injector(s) and/or from the high-pressure fuel pump, and a pressure control in the return line controls pressure in the return line as a function of the delivery pressure of the presupply pump.
In this fuel injection system, the pressure maintenance in the return line is improved by virtue of the fact that the delivery pressure of the presupply pump is used as a reference value for the pressure control in the return line. Since the delivery pressure of the presupply pump is controlled, the control performance of the pressure in the return line is also improved.
In a modification of the invention, the delivery pressure of the presupply pump is controlled to an absolute value so that the control of pressure in the return line is also independent of the ambient pressure and an improvement in the control performance is consequently achieved.
Another modification of the invention includes the provision that the presupply pump is disposed in the tank. A tank jet pump for filling a collection cup is provided in the tank, and that the return line drives the tank jet pump. In this embodiment, the presupply pump is driven independently of the high-pressure fuel pump and can therefore be better controlled. As a result, the pressure in the pressure region of the presupply pump is kept constant to a better degree, which has an advantageous effect on the control performance of the pressure in the return line.
In another modification of the invention, the pressure control valve has at least one inlet, an outlet, and a control pressure connection and the control pressure connection is hydraulically connected to the pressure side of the presupply pump so that the control performance of the pressure in the return line is improved in the manner according to the invention.
One embodiment of the invention also includes the provision that the pressure control valve is embodied as a sliding valve, that one end of the slider is subjected to the delivery pressure of the presupply pump, that a second end of the slider is subjected to the pressure of the return line and the force of a control spring, and that depending on the position of the slider, the outlet of the pressure control valve is unblocked so that the pressure in the return line can be controlled in a simple manner. The sensitive reaction behavior of slide valves permits particularly high control performance to be achieved.
Another embodiment of the invention includes the provision that the pressure control valve is embodied as a seat valve with a diaphragm and valve body, that a first side of the diaphragm is subjected to the delivery pressure of the presupply pump, that a second side of the diaphragm is also subjected to the pressure of the return line and the force of a control spring, and that depending on the position of the diaphragm, the valve body for a valve seat is lifted up and the outlet of the pressure control valve is unblocked so that due to the size of the diaphragm, even extremely small pressure changes trigger a control action and consequently, a high control performance is achieved.
The valve body can be embodied as a ball or a valve cone so that the specific advantages of these valve bodies can also be used for a fuel injection system according to the invention.